Abstract:
A field experiment was conducted during 2001-2003 to evaluate the
effect of water stress on the yield and yield components of four rice
cultivars commonly grown in Mazandaran province, Iran. In northern Iran
irrigated lowland rice usually experiences water deficit during the growing
season include of land preparation time, planting, tillering stage, flowering
and grain filing period. Recently drought affected 20 of 28 provinces
in Iran; with the southeastern, central and eastern parts of the country
being most severely affected. The local and improved cultivars used were
Tarom, Khazar, Fajr and Nemat. The different water stress conditions were
water stress during vegetative, flowering and grain filling stages and
well watered was the control. Water stress at vegetative stage significantly
reduced plant height of all cultivars. Water stress at flowering stage
had a greater grain yield reduction than water stress at other times.
The reduction of grain yield largely resulted from the reduction in fertile
panicle and filled grain percentage. Water deficit during vegetative,
flowering and grain filling stages reduced mean grain yield by 21, 50
and 21% on average in comparison to control respectively. The yield advantage
of two semidwarf varieties, Fajr and Nemat, were not maintained under
drought stress. Total biomass, harvest index, plant height, filled grain,
unfilled grain and 1000 grain weight were reduced under water stress in
all cultivars. Water stress at vegetative stage effectively reduced total
biomass due to decrease of photosynthesis rate and dry matter accumulation.